Journal of Colloid and Interface Science 315 (2007) 142–157 www.elsevier.com/locate/jcis Feature article Nanofibrous and nanotubular supports for the immobilization of metalloporphyrins as oxidation catalysts Shirley Nakagaki, Fernando Wypych ∗ Universidade Federal do Paraná, Departamento de Química, CP 19081, CEP 81531990, Curitiba, Paraná, Brazil Received 4 April 2007; accepted 19 June 2007 Available online 22 June 2007 Abstract Nanofibrous and nanotubular materials, natural and synthetic, are important alternative matrices for the immobilization of metallocomplexes, especially metalloporphyrins, as oxidation catalysts. The process permits a regular and controllable distribution of the active phase at the outer and/or inner surfaces of the tubes, promoting a special environment for the approximation of a substrate to the catalytic active species. The im- mobilization also prevents the molecular aggregation and bimolecular self-destruction reactions, facilitates the recovery and reuse of the catalyst, reduce de cost of material preparation and environmental concerns. A variety of nanofibrous and nanotubular structures are presented and specific examples of immobilization of iron porphyrins in different supports and their oxidation catalytic activities are presented and discussed.  2007 Elsevier Inc. All rights reserved. Keywords: Porphyrins; Immobilization; Oxidation catalysis; Fibrous and tubular matrixes 1. Introduction The strategy of mimic enzymatic systems has become an extensive research area of synthetic porphyrins, and other co- ordination complexes, as models of enzyme active sites. The main efforts are concentrated especially on monoxygenase en- zymes of the cytochrome P-450 family since the catalytic activ- ity behavior of this enzyme family has inspired the design and synthesis of various mineral (inorganic) complexes with poten- tial application in the chemical industry for oxidation reactions and many other uses such as in electrochemical applications and chemical sensors [1,2]. Studies of selectivity and stability presented by the synthetic models compared to natural systems (cytochrome P-450), in the biomimetic oxidation of hydrocarbons, suggested that se- lectivity not only arises from the steric effects imposed by the environment of the enzyme active site upon substrate ap- proach, but also from specific binding at the active site, amongst other factors [3,4]. The monooxygenase cytochrome P-450 has a heme-enzime catalytic site that catalyses a variety of aerobic * Corresponding author. E-mail address: wypych@quimica.ufpr.br (F. Wypych). oxidations mediated by a reducing agent. The catalytic cycle of the enzyme has been proposed for many different research groups based on biological studies, synthesis of model com- pound studies and spectroscopic analyses. An example of the mechanism of the action of the enzyme is illustrated in Fig. 1. The active specie assumed in the catalytic oxidation of dif- ferent substrate by the enzyme is a high valence iron-oxo, (6) resulting by the previously iron–dioxygen interaction fol- lowing by the O–O bond cleavage (2–5). Besides the dioxygen molecule as oxygen donor to the effective cytochrome P-450 oxidation mechanism, the enzyme (1) and its metalloporphyrin model complexes can promote reactions by oxidants such as io- dosylbenzene, alkyl and hydrogen peroxide or peracid (Fig. 1, shunt path). In the last 30 years different porphyrins structures were synthesizes in order to reproduce the shunt path in the cat- alytic active cycle. Many research groups modified the porphyrin structure in order to design and synthesize resistant structures that mimic the efficiency and selectivity observed in the biological systems. Many of these structural modifications were done in order to mimic the protein cavity of natural enzymes [5]. The immobilization of metalloporphyrins carrying electron- withdrawing substitutes on mineral supports has been found efficient when used as a selective catalyst for oxidation of hy- 0021-9797/$ – see front matter  2007 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2007.06.032